Astrocytic straight tubules in the brain of a patient with Pick's disease

Cellular Biology of Tau Diversity and Pathogenic Conformers

Tau accumulation is a prominent feature in a variety of neurodegenerative disorders and remarkable effort has been expended working out the biochemistry and cell biology of this cytoplasmic protein. Tau's wayward properties may derive from germline mutations in the case of frontotemporal lobar degeneration (FTLD-MAPT) but may also be prompted by less understood cues—perhaps environmental or from molecular damage as a consequence of chronological aging—in the case of idiopathic tauopathies. Tau properties are undoubtedly affected by its covalent structure and in this respect tau protein is not only subject to changes in length produced by alternative splicing and endoproteolysis, but different types of posttranslational modifications that affect different amino acid residues. Another layer of complexity concerns alternate conformations—“conformers”—of the same covalent structures; in vivo conformers can encompass soluble oligomeric species, ramified fibrillar structures evident by light and electron microscopy and other forms of the protein that have undergone liquid-liquid phase separation to make demixed liquid droplets. Biological concepts based upon conformers have been charted previously for templated replication mechanisms for prion proteins built of the PrP polypeptide; these are now providing useful explanations to feature tau pathobiology, including how this protein accumulates within cells and how it can exhibit predictable patterns of spread across different neuroanatomical regions of an affected brain. In sum, the documented, intrinsic heterogeneity of tau forms and conformers now begins to speak to a fundamental basis for diversity in clinical presentation of tauopathy sub-types. In terms of interventions, emphasis upon subclinical events may be worthwhile, noting that irrevocable cell loss and ramified protein assemblies feature at end-stage tauopathy, whereas earlier events may offer better opportunities for diverting pathogenic processes. Nonetheless, the complexity of tau sub-types, which may be present even within intermediate disease stages, likely mitigates against one-size-fits-all therapeutic strategies and may require a suite of interventions. We consider the extent to which animal models of tauopathy can be reasonably enrolled in the campaign to produce such interventions and to slow the otherwise inexorable march of disease progression.

Molecular Pathogenesis of the Tauopathies

The tauopathies constitute a group of diseases that have Tau inclusions in neurons or glia as their common denominator. In this review, we describe the biochemical and histological differences in Tau pathology that are characteristic of the spectrum of frontotemporal lobar degeneration as primary tauopathies and of Alzheimer's disease as a secondary tauopathy, as well as the commonalities and differences between the familial and sporadic forms. Furthermore, we discuss selected advances in transgenic animal models in delineating the different pathomechanisms of Tau.

Protein astrogliopathies in human neurodegenerative diseases and aging

Neurodegenerative diseases are characterized by progressive dysfunction and loss of neurons associated with depositions of pathologically altered proteins showing hierarchical involvement of brain regions. The role of astrocytes in the pathogenesis of neurodegenerative diseases is explored as contributors to neuronal degeneration or neuroprotection pathways, and also as potential mediators of the transcellular spreading of disease-associated proteins. Protein astrogliopathy (PAG), including deposition of amyloid-β, prion protein, tau, α-synuclein, and very rarely transactive response DNA-binding protein 43 (TDP-43) is not unprecedented or unusual in neurodegenerative diseases. Morphological characterization of PAG is considered, however, only for the neuropathological diagnosis and classification of tauopathies. Astrocytic tau pathology is seen in primary frontotemporal lobar degeneration (FTLD) associated with tau pathologies (FTLD-Tau), and also in the form of aging-related tau astrogliopathy (ARTAG). Importantly, ARTAG shares common features with primary FTLD-Tau as well as with the astroglial tau pathologies that are thought to be hallmarks of a brain injury-related tauopathy known as chronic traumatic encephalopathy (CTE). Supported by experimental observations, the morphological variability of PAG might reflect distinct pathogenic involvement of different astrocytic populations. PAG might indicate astrocytic contribution to spreading or clearance of disease-associated proteins, however, this might lead to astrocytic dysfunction and eventually contribute to the degeneration of neurons. Here, we review recent advances in understanding ARTAG and other related forms of PAG.

RETRACTED: Wild type and P301L mutant Tau promote neuro-inflammation and α-Synuclein accumulation in lentiviral gene delivery models

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concerns about the article were raised on PubPeer [https://pubpeer.com/publications/DA4525FDCD8F7FEA2E4ACC9EC9322F] namely that in the western blots there are similarities between Fig. 1D and 1E, Fig. 2B duplicates Fig. 3E, Fig. 4L duplicates Fig. 5A and Fig. 4A partly duplicates Fig. 4F, and Figure 2D is the same as Figure 1B in Algarzae, N., Hebron, M., Miessau, M., Moussa, C.E.H., 2012. Parkin prevents cortical atrophy and Ab-induced alterations of brain metabolism: 13C NMR and magnetic resonance imaging studies in AD models. Neuroscience 225, 22-34. The corresponding author was not able to provide the raw data, and therefore requested to retract the article. Authors Charbel E.-H. Moussa, G. William Rebeck and Alexander M. Herman agreed to this retraction, Preeti J. Khandelwal and Sonya B. Dumanis are no longer in science and could not be contacted.

The Relationship between Parkin and Protein Aggregation in Neurodegenerative Diseases

The most prominent changes in neurodegenerative diseases are protein accumulation and inclusion formation. Several neurodegenerative diseases, including Alzheimer's, the Synucleinopathies and Tauopathies share several overlapping clinical symptoms manifest in Parkinsonism, cognitive decline and dementia. As degeneration progresses in the disease process, clinical symptoms suggest convergent pathological pathways. Biochemically, protein cleavage, ubiquitination and phosphorylation seem to play fundamental roles in protein aggregation, inclusion formation and inflammatory responses. In the following we provide a synopsis of the current knowledge about protein accumulation and astrogliosis as a common denominator in neurodegenerative diseases, and we propose insights into protein degradation and anti-inflammation. We review the E3-ubiquitin ligase and other possible functions of parkin as a suppressant of inflammatory signs and a strategy to clear amyloid proteins in neurodegenerative diseases.

Pick's disease: a modern approach

Pick's disease is a rare dementing disorder that is sometimes familial. The cardinal features are circumscribed cortical atrophy most often affecting the frontal and temporal poles and argyrophilic, round intraneuronal inclusions (Pick bodies). Clinical manifestations reflect the distribution of cortical degeneration, and personality deterioration and memory deficits are often more severe than visuospatial and apraxic disorders that are common in Alzheimer's disease, but clinical overlap with other non-Alzheimer degenerative disorders is increasingly recognized. Neuronal loss and degeneration are usually maximal in the limbic system, including hippocampus, entorhinal cortex and amygdala. Numerous Pick bodies are often present in the dentate fascia of the hippocampus. Less specific features include leukoencephalopathy and ballooned cortical neurons (Pick cells). Glial reaction is often pronounced in affected cerebral gray and white matter. Tau-immunoreactive glial inclusions are a recently recognized finding in Pick's disease, and neuritic changes have also recently been described. Variable involvement of the deep gray matter and the brainstem is typical, with a predilection for the monoaminergic nuclei and nuclei of the pontine base. Neurochemical studies demonstrate deficits in intrinsic cortical neurotransmitter systems (e.g., somatostatin), but inconsistent loss of transmitters in systems projecting to the cortex (e.g., cholinergic neurons of the basal nucleus). Biochemical and immunocytochemical studies have demonstrated that abnormal tau proteins are the major structural components of Pick bodies. A specific tau protein immunoblotting pattern different from that seen in Alzheimer's disease and certain other disorders has been suggested in some studies. A specific molecular marker and a genetic locus for familial cases are not known.

Tau-positive glial inclusions in progressive supranuclear palsy, corticobasal degeneration and Pick's disease

The presence of tau-positive glial inclusions has been recently found a consistent feature in the brains of patients with progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Pick's disease (PiD). These inclusions are classified based on cellular origin as tau-positive astrocytes, presumably either fibrillary or protoplasmic, coiled bodies and glial threads. Immunohistochemically, their major structural component is abnormal tau proteins, similar to those found in Alzheimer's disease. Nevertheless, their morphology, including ultrastructural profile, has been suggested to be distinctive for each disease. The profile and extent of particular glial inclusions correlate well with disease phenotype. Highly characteristic correlations include tufts of abnormal fibers in PSP, astrocytic plaques and dense glial threads in CBD and ramified astrocytes and small Pick body-like inclusions in PiD. The significance of the inclusions in disease pathogenesis and their biochemical characteristics remain to be clarified. Nevertheless, these distinctive glial lesions most likely reflect fundamental alterations in isoform composition of tau as well as its specific cellular and regional expression in sporadic tauopathies.

Tau-Positive Fine Granules in the Cerebral White Matter: A Novel Finding Among the Tauopathies Exclusive to Parkinsonism-Dementia Complex of Guam

We examined the autopsied brains of cases of 6 types of tauopathy: parkinsonism-dementia complex of Guam (PDC), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), Pick disease, Alzheimer disease (AD), and myotonic dystrophy together with Guamanian controls. Light microscopy sections of these brains were examined using anti-tau antibodies. Tau-positive fine granules (TFGs) were globe-shaped, and 3 to 6 mum in diameter, were observed predominantly in the frontal white matter in 30 of the 35 patients with PDC. However, no TFGs were found in association with PSP, myotonic dystrophy, Pick disease, AD, or CBD. Western blot analysis of frozen brain tissue taken from the PDC cases revealed that the frontal cortex was hyperphosphorylated and contained 6 tau isoforms (3R+4R tau). However, in the present study, it was revealed that the novel TFGs in the white matter of patients with PDC was composed of 4R tau. Western blot analysis of sarkosyl-insoluble tau from the white matter of the PDC cases showed 2 major bands of 60 and 64 kDa and one minor band of 67 kDa. After dephosphorylation, these bands resolved into one major band of 4-repeat (4R) tau isoform and 3 minor bands of 3-repeat (3R) and 4R tau isoforms. Moreover, the TFGs observed in cases in which the number of neurofibrillary tangles (NFTs) was higher than the threshold level were not correlated with the presence of cortical NFTs. In conclusion, these novel TFGs were found almost exclusively in PDC brains and could therefore be considered as a characteristic neuropathologic marker of this particular tauopathy. The TFGs were hyperphosphorylated tau-positive structures that may be formed by a different mechanism from that used to produce cortical NFTs.

Tau and axonopathy in neurodegenerative disorders

The microtubule (MT)-associated protein (MAP) tau in neurons has been implicated as a significant factor in the axonal growth, development of neuronal polarity, and the maintenance of MT dynamics. Tau is localized to the axon, and is known to promote MT assembly and to stabilize axonal MTs. These functions of tau are primarily regulated by the activities of protein kinases and phosphatases. In Alzheimer's disease and other neurodegenerative disorders, abundant filamentous tau inclusions are found to be major neuropathological characteristics of these diseases. Both somato-dendritic and axonal tau lesions appear to be closely associated with axonal disruption. Furthermore, recent discoveries of pathogenic mutations on the tau gene suggest that abnormalities of tau alone are causative of neurodegeneration. Finally, analyses of transgenic mice that express human tau proteins have enabled in vivo quantitative assessments of axonal functions and have provided information about mechanistic relationships between pathological alteration of tau and axonal degeneration.

Transgenic mouse model of tauopathies with glial pathology and nervous system degeneration

Frontotemporal dementias (FTDs), including corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), are neurodegenerative tauopathies characterized by widespread CNS neuronal and glial tau pathologies, but there are no tau transgenic (Tg) mice that model neurodegeneration with glia tau lesions. Thus, we generated Tg mice overexpressing human tau in neurons and glia. No neuronal tau aggregates were detected, but old mice developed Thioflavin S- and Gallyas-positive glial tau pathology resembling CBD astrocytic plaques. Tau-immunoreactive and Gallyas-positive oligodendroglial coiled bodies (similar to CBD and PSP), glial degeneration, and motor deficits were associated with age-dependent accumulations of insoluble hyperphosphorylated human tau and tau immunopositive filaments in degenerating glial cells. Thus, tau-positive glial lesions similar to human FTDs occur in these Tg mice, and these pathologies are linked to glial and axonal degeneration.

Preservation of nigral neurons in Pick's disease with Pick bodies: a clinicopathological and morphometric study of five autopsy cases

Many reports have described loss of neurons in the substantia nigra in Pick's disease (PiD). In those reports, however, "Pick's disease" includes PiD without Pick bodies (PB), and there is only limited data available on regional nigral pathology in PiD with PB. To elucidate the pathological changes of the substantia nigra in PiD with PB, we examined five cases and 12 age-matched controls by morphometry. The number and size of pigmented and nonpigmented neurons, as well as the area of the substantia nigra were examined. The area of the substantia nigra was significantly reduced in PiD with PB. The pigmented and nonpigmented neuron counts in PiD with PB were not statistically different from those in controls. There was a significant reduction in the size of pigmented neurons in PiD with PB to 82% with that in the controls. In addition, after reviewing 48 cases of PiD with PB reported in the literature, we found that none of the cases with typical frontotemporal lobe symptoms exhibited parkinsonism until the terminal stage. These data are useful for discriminating PiD with PB from other diseases showing frontotemporal characteristics, including the frontal lobe degeneration type and the motor neuron disease type of frontotemporal dementia.

Unique astrocytic inclusion in a 2 month-old baby showing Leigh-like brain lesions with lactic acidosis

An unique cytoplasmic inclusion was found in astrocytes of a 2-month-old female baby who showed Leigh-like brain lesions with lactic acidosis, hypoglycemia and hepatomegaly. Although a defective enzyme was not determined, a metabolic disorder was suggested from clinicopathological observations. Symmetrically distributed lesions consisting of marked gliosis and proliferation of capillaries were observed in the basal ganglia, thalami and tegmentum. The astrocytic cytoplasmic inclusion was exclusively found in the cerebral and cerebellar white matter, where myelination was immature. The inclusion was round and eosinophilic, and positive for glial fibrillary acidic protein, vimentin, alphaB-crystallin, S-100 protein and microtubule associated protein 1B, immunohistochemically. An electron microscopic examination revealed an accumulation of intermediate filaments, ribosome and rough endoplasmic reticulum in the inclusion. The characteristic of this inclusion is different from that of other reported inclusions. The inclusion showed positive immunoreaction against CuZn superoxide dismutase, catalase, advanced glycation end-product and 4-hydroxy-2-nonenal antibodies, which suggest that oxidative stress is involved in the genesis of the inclusion.

Involvement of precerebellar nuclei in Pick's disease

Pick's disease is a progressive degenerative disorder of the human brain which involves not only numerous areas of the cerebral cortex but also a characteristic set of subcortical nuclei. The disorder is associated with the formation of abnormal and hyperphosphorylated tau protein, which occurs in only a few susceptible neuronal types and leads to major cytoskeletal alterations. Preferentially affected by the destructive process are small nerve cells of both cortical areas and subcortical nuclei. Immunoreactions for abnormally phosphorylated tau protein permit identification of the alterations in their entirety. In an initial step in their development, patches of a nonargyrophilic material appear, irregularly filling both the somata and neurites of afflicted cells. The abnormal material is then partially converted into condensed spindle-shaped or spherical structures, which gradually become significantly argyrophilic. Globose argyrophilic Pick bodies eventually appear within the somata, and small Pick neurites of variable sizes and shapes develop in varicose expansions of the dendritic processes. Silver staining reveals only a fraction of the abnormal material and is adequate only for diagnostic purposes, while immunostaining of the abnormal tau protein discloses the complete neuropathological picture. The present study points to a conspicuous affliction of specific precerebellar nuclei in Pick's disease. Immunoreactive punctae, probably corresponding to terminal synaptic boutons of afferent fibers, appear at sites in the inferior olive receiving intense input from the cerebral cortex. The brunt of the changes, however, are borne by the pontine gray, the arcuate nucleus, the pontobulbar body, and the paramedian reticular nucleus. Altered areas show immunoreactive punctae and an abundance of small immunoreactive nerve cells partially containing Pick bodies and Pick neurites. Again, a feature common to all the affected nuclei is that they receive major input from the cerebral cortex, while other precerebellar nuclei with preponderant input from the spinal cord and/or other noncortical sources remain unscathed or exhibit only sparse involvement. The lesional pattern which develops in specific precerebellar nuclei is interpreted to be a partial reflection of the cortical involvement of Pick's disease.

Region- and cell-type-specific pattern of tau phosphorylation in dog brain

A study of brains of 16 dogs from one to 19 years of age showed a structure- and cell-type- specific pattern of tau protein phosphorylation at mAb Tau-1 site and the absence of phosphorylation at the mAb AT8 site. Strong immunolabeling with mAb Tau-1 of the mossy fibers and perikarya of neurons in sectors CA3 and CA4 of the cornu Ammonis, less intensive staining in the cytoplasm in neocortical and subcortical neurons, and selective staining of some pyramidal cells in sectors CA1 and CA2 show differences in the amount of phosphorylated tau, not only in different types of neurons, but also in different parts of the cell. The immunoreactivity of oligodendrocytes and the absence of the reaction in astrocytes reflect differences in tau phosphorylation in glial cells. Marked immunoreactivity in 13 dogs but minimal reaction in brains of three other dogs appears to reflect interindividual differences, which are associated presumably with genetic background. Shrinkage of neurons, tortuosity of mossy fibers, accumulation of phosphorylated tau in the nucleoplasm, and deformation of the nuclei of neurons and oligodendrocytes suggest that excessive phosphorylation at the mAb Tau-1 site is associated with neuronal and oligodendrocyte degeneration and, possibly, cell death.

Recent advances in dementia research in Japan: non-Alzheimer-type degenerative dementias

In this article, we review recent reports by Japanese researchers on non-Alzheimer-type degenerative dementias. These dementias can be classified into the following subtypes: dementias with Lewy bodies, including diffuse Lewy body disease, dementias with neurofibrillary tangles, dementias with glial tangles, including progressive supranuclear palsy and corticobasal degeneration, argyrophilic grain dementia, frontotemporal dementias including Pick's disease; dementias with degeneration of subcortical nuclei, including Huntington's disease and, last, unclassified dementias. Recently, these various forms of dementia have received much attention in Japan, as elsewhere.

Neurodegenerative disorders with extensive tau pathology: a comparative study and review

Many neurodegenerative disorders with onset in mid to late adult life present diagnostic challenges to clinicians and pathologists alike. A distinguishing neuropathological feature has traditionally been the presence or absence of neurofibrillary tangles. Recent biochemical and molecular biological studies have identified the microtubule-binding protein tau as the predominant component of these and related inclusions, and have provided powerful new reagents for the study of neurodegenerative diseases. Several diseases previously considered distinct pathophysiological entities contain similar tau-immunoreactive lesions, but qualitative and regional anatomical differences in vulnerability can differentiate the disorders. Comparison of tau-immunoreactive lesions in three relatively uncommon neurodegenerative diseases-progressive supranuclear palsy, Pick's disease, and corticobasal degeneration-illustrates the types of analyses that demonstrate unexpected pathological similarities, but also fundamental differences between these disorders. These results have important implications for the differential diagnosis of disorders containing tau-immunoreactive lesions, including Alzheimer's disease.

Cytoskeletal pathology in non-Alzheimer degenerative dementia: new lesions in diffuse Lewy body disease, Pick's disease, and corticobasal degeneration

Increasing use of immunocytochemistry for evaluation of dementia disorders has revealed histopathological alterations that were previously unknown, even with sensitive silver techniques. Disorders [Pick's disease (PD), diffuse Lewy body disease (DLBD) and corticobasal degeneration (CBD)] in which immunocytochemistry has revealed occult pathology are discussed. All three disorders have neurofilament (NF) immunoreactive neuronal alterations in the neocortex. In DLBD round, eosinophilic cytoplasmic inclusions referred to as cortical Lewy bodies are neurofilament-positive, while in both PD and CBD neurofilament epitopes are expressed in irregularly swollen neurons and their proximal cell processes, which are referred to as ballooned neurons. Interestingly, the cortical neuronal population that is vulnerable to Lewy bodies is similar to that which is vulnerable to ballooned neurons. Furthermore, Lewy bodies can occasionally be detected within the cytoplasm of ballooned neurons. Besides neurofilament-immunoreactivity, Lewy bodies are immunoreactive for ubiquitin, while ballooned neurons are inconsistently stained with antibodies to ubiquitin. Both Lewy bodies and ballooned neurons can be appreciated with routine histology, but they are much easier to detect with immunocytochemistry. In contrast, a new type of neuritic alteration in the hippocampal CA2/3 region has been recognized in DLBD. These dystrophic neurites cannot be appreciated with routine histology and are only optimally seen with immunocytochemistry for ubiquitin. Their presence is a certain indication of the presence of cortical Lewy bodies. The microtuble associated protein tau is the major constituent of neurofibrillary tangles in Alzheimer's disease (AD). Biochemical studies have shown that Pick bodies, argyrophilic neuronal inclusions that are highly characteristic of, if not pathognomonic for PD are also composed of abnormal tau protein. Along with Pick bodies, tau has recently been detected in glial cells in PD. Similar so-called "gliofibrillary tangles" are increasingly recognized in progressive supranuclear palsy. Previously, CBD was considered to be free of such lesions, but recent studies have revealed widespread tau-positive neuronal and glial cytoskeletal lesions in CBD. A distinctive type of tau-positive glial lesion in CBD is characterized by annular clusters of grain-like tau immunoreactivity reminiscent of a neuritic plaque in AD, except that the clusters are devoid of amyloid. The tau-positive profiles are consistently located around a central astrocyte cell body. Double labeling studies with glial fibrillary acidic protein, vimentin and CD44, which are markers for reactive astrocytes, demonstrates tau immunoreactivity within astrocytic processes; these "astrocytic plaques" appear to be specific for CBD. Although NF, ubiquitin and tau proteins are present in diverse neuronal and glial inclusions in these disorders, the morphology and distribution of these lesions differentiate non-AD dementias.

Thorn-shaped astrocytes: possibly secondarily induced tau-positive glial fibrillary tangles

Argyrophilic and tau-positive abnormal structures occurring in glial cells are called glial fibrillary tangles. In the astrocyte, a conspicuous tau-positive structure is known to appear in progressive supranuclear palsy (PSP). In this report, another type of argyrophilic and tau-positive astrocytes is reported. The morphology of this new type is quite different from that of the previously reported tau-positive astrocyte in PSP and they are designated here as thorn-shaped astrocytes (TSA). TSA have an apparently argyrophilic cytoplasm with a few short processes and often have a small eccentric nucleus, whose appearance resembles that of a reactive astrocyte. Immunohistochemically, TSA are positive to anti-tau antibodies but are negative for ubiquitin. Simultaneous immunostaining revealed the coexistence of tau and glial fibrillary acidic protein epitopes in the same cytoplasm. Electron microscopically, bundles of 15-nm straight tubules were included in the cytoplasm together with abundant glial filaments. In the vicinity of a cluster of TSA, related structures of perivascular or subpial tau-positive linings, which correspond to astrocytic end-feet, are sometimes observed. In almost all cases, a few TSA are generally located in a confined area of subpial and subependymal regions. Although TSA appear to be intimately associated with some diseases, they are also found in a wide range of cytoskeletal disorders including the aged brain with neurofibrillary tangles. TSA are presumed to be a secondary induced product in relation to astrocytic reaction.

Paired helical filaments and straight tubules in astrocytes: an electron microscopic study in dementia of the Alzheimer type

Ultrastructural investigation of the hippocampal CA1 and CA4 of nine autopsy-proven cases of dementia of the Alzheimer type (duration of disease: 3-16 years; age: 76-92 years) revealed paired helical filaments (PHFs) and straight tubules (STs) in astrocytes of three advanced cases of long duration (> 13 years). The PHFs and STs were indistinguishable from those seen in neurons. The abnormal glial fibrils were confined to the astrocytic processes that were associated with small vessels or, more frequently, with ghost tangles. In both locations the astrocytic PHFs and STs were located in the cytoplasm without limiting membranes, and were thicker than the straight filaments that composed ghost tangles. These findings, combined with the presence of regular constrictions of astrocytic PHFs, suggest that abnormal astrocytic fibers are produced by the glial cells, not engulfed by them. In addition, the presence of these abnormal glial filaments in only advanced, long-duration cases of dementia of the Alzheimer type suggests that disease duration has a significant effect upon the formation of these astrocytic profiles.